ORIGIN OF URANIUM MINERALIZATION IN UNCONVENTIONAL GEOLOGICAL SETTINGS

Michel CUNEY

UNIVERSITE DE LORRAINE – GEORESSOURCESCREGU – CNRS

54 506, Vandoeuvre les NANCY FRANCE

METAMORPHICROCKS

M A N T L E

T °C

100100

200

300

400

600

25

800

CONTINENTAL

CRUST

Upper cont. crust

Primitive Mantle : 21ppb

Carb. chondrites : 7ppb

METAMORPHICROCKS

M A N T L E

T °C

100100

200

300

400

600

25

800

Primitive mantle : 21ppbCarb. chondrites : 7ppb

Calcretes/Lignite/Coal

PhosphatesBlack Shales

Conglomerates

RollfrontBasal

Breccia

TabularTectonolithologic

UnconformityPipes

HTMetamorphic

Na-metasomatism

LTMetamorphic

SEDIMENTARYROCKS

IGNEOUSROCKS

MagmaticMagmatic(crystal. fract)(

Veins

Volcanic

IOCG(U)

1.4 ppm U

2.7 ppm U

Enriched mantleHKCa

PAl

PAk

PAl

HKCa

.

HKCa

PAl

PAk

PAl

HKCaPAk

Depleted mantle

Alaskites

Skarns

Unconventional resourcesResources from which uranium is only recoverable as a minor by-product, such as :

� black shales and lignite,�uranium associated with phosphate rocks,� seawater� non-ferrous ores (porphyry copper, …), � carbonatite, � peralkaline intrusions, by product of REE production ?� monazite placers

A GENETIC CLASSIFICATION OF U-DEPOSITS (i)- I (M) MAGMATIC

• I.1 (MFC) fractional crystallization peralkaline Kvanefjeld, Greenland 135,000t@ 220ppm

• I.2 (MPM) partial melting granitic pegmatoids Rössing Namibia 246,500tU @300ppm

- II (H) HYDROTHERMAL

• II.1 (HV) hydrothermal-volcanic Streltsovkoye caldera (Russia): 250,000 t U at 0.10%

• II.2 (HG) hydrothermal-granitic Aue-Niederschlema, Germany 100,000 t U

• II.3 (HD) hydrothermal-diagenetic diagenetic brine circulation 3 sub-categories:

•II.3a (HDIa) with intraformational redox control:

o(HDIaTb) tabular Grants region, Colorado >240,000 t U @ 0.09-0.21 % mined

o(HDIaTl) tectonolithologic Lodève basin, France.

o(HDIaCb) dissolution-collapse breccias pipes Gd Canyon Arizona, USA

• II.3b (HDBb) with basement/basin redox control Athabasca, E Alligator River

• II.3c (HDIr) interformational redox boundary, Oklo, Gabon 27,635tU@0.38%

• II.4 (HMp) hydrothermal-metamorphic Shinkolobwe DRC 25 500tU, 0.40%

A GENETIC CLASSIFICATION OF U-DEPOSITS (ii)• II.5 (HMt) Hydrothermal-metasomatic

• II.5a (HMtNa) Na-metasomatism central Ukraine 180,000 t U

• II.5b (HMtK) K-metasomatism Elkon (Aldan, Russia) > 324,000tU@0.1-0.15 % U±Au

• II.5c (HMtSk) Skarn-related contact/regional met. Mary Kathleen 8550tU@0.11 %

- III (M) METEORIC WATER INFILTRATION with two sub-types:• III.1 (MB) Basal-type paleovalley or infiltration-type in Russia, Vitim district• III.2 (MRf) Roll fronts Kazakhstan with over 1 M t U resources

- IV (S) SYNSEDIMENTARY subdivided into 4 major types• IV.1 (SMs) Mechanical sorting Quartz Pebble Conglomerates Monazite placers• IV.2 (SRtm) Redox trapping in marine environments black shales. Sweden > 1 M t U

• IV.3 (SRtc) Redox trapping in contin envir coal, lignite, peat bog, swamp, anoxic lake

• IV.4 (SCcr) Crystal-chemical and redox trapping phosphorites up to 15-22 M t U

- V (E) EVAPOTRANSPIRATION = calcretes Langer Heinrich, Namibia 63 520 tU @ 510 ppm

- VI (O) OTHER TYPES Olympic Dam Fe-ox Cu-Au(U-Ag) (IOCG) S. Aust. 1.9 MtU @340ppm

� Peralkaline complexes

� Carbonatites (Palaborwa, South Africa)

� Intrusive U deposits (IAEA classif.) Porphyry Cu

(high-K calc-alkaline granites)

U deposits related to crystal fractionation

ppm Ultrabasic Basic Intermediate Granites X

U 0.021 0.75 2.4 3.3 x 160

Th 0.060 3.5 7.8 17.5Earth average Th/U = 4

INCOMPATIBLE BEHAVIOR

URANIUM FRACTIONATION FROM ULTRABASIC ROCKS TO GRANITES

U INCOMPATIBLE BEHAVIOUR

� several major geochemical and metallogenic consequences:

(i) U continuously transferred from the mantle to the Earth crust, & within the continental crust towards its upper part together with Th, K, …

(ii) the most felsic melts tend to be the most enriched in U,

(iii) granites & rhyolites � primary U sources for the formation of most U deposits, also unconventional deposits

Average granite (U= 3-4 ppm), U mainly in zircon, apatite, monazite, titanite, … from which U cannot be leached by most geological fluids � U enriched granites are needed as an efficient U source

Fondamental U fractionation processesI

O

N

I

C

R

D

I

U

S

COMPATIBLE

CORE

MAIN COORDINANCE

K-FELDSPAR –K-MICAS

ACCESSORYMINERALS

VALENCY1 2 3 4 5 6

1.5

12

8

6

4

0

0.5

1

2

< 1

> 50

15 – 50

1 – 15

Th 167U 156Zr 23Hf 21

Cr< 1

Se < 1

Ni < 1 V < 1 Ir < 1Os < 1

Pt < 1Ti < 1

Cu< 1

Al 4

Fe < 1Mn < 1

Mg < 1Sc < 1

Cs 205Rb 204

Ba 108K 156

Pb 167La 54

Ce 45 Pr 34Sm 43Nd 34

Y 6Lu 6

Na 12Sr 20

Ca 1

Mo 25

CONTINENTAL CRUST / C - CHONDRITE

COMPATIBLE

CORE

MAIN COORDINANCE

K-FELDSPAR –K-MICAS

VALENCY1 2 3 4 5 61 2 3 4 5 6

1.5

12

8

6

4

0

0.5

1

2

12

8

6

4

0

0.5

1

2

< 1

> 50

15 – 50

1 – 15

Th 167U 156Zr 23Hf 21

Cr< 1

Se < 1

Ni < 1 V < 1 Ir < 1Os < 1

Pt < 1Ti < 1

Cu< 1

Al 4

Fe < 1Mn < 1

Mg < 1Sc < 1

Cs 205Rb 204

Ba 108K 156

Pb 167La 54

Ce 45 Pr 34Sm 43Nd 34

Y 6Lu 6

Na 12Sr 20

Ca 1

Mo 25

CONTINENTAL CRUST / C - CHONDRITE

HFSE : HIGH FIELD STRESS ELEMENTS

Nb 45Ta 55Nb 45Ta 55

LILE : LARGE ION LITHOPHILE ELEMENTS

Al/(Na+K+2Ca) = A/CNK in cations= ASI Aluminium Saturation Index

Al/(Na+K) ou (Na+K) Al = AGPAICITY

why ?

= INDEX OF MAGMA POLYMERISATION

Magma aluminous indices to classify magmatic rocks

U-rich magma classification using aluminous indicessome specific granites have higher U contents

IMPOSSIBLECOMPOSITION

FIELD

PERALUMINOUS

PERALCALINE

METALUMINOUS

Al/(N

a+K)

Leucogranites(two micas)S-Type

High-KCalc-alkaline

A2 Type

quartz saturated& undersaturatedseries

A1 Type

feldspars

1.11

Al/(Na+K+2Ca)

Al/(Na+K) = 1 &Al/(Na+K+2Ca) = 1

whenAl-Na-K-Ca in feldspars only

Al/(Na+K+2Ca) > 1

� peraluminous

Al/(Na+K+2Ca) < 1

& Al/(Na+K) < 1

� peralkaline

Al/(Na+K+2Ca) >1

& Al/(Na+K) > 1

� calc-alkaline

1 .41 .00 .6 1 .81 0 0

1 0 1

1 0 2

1 0 3

1 0 4

1 0 5

Na+K/Al

Na2 CO3

HCl

NaCl

UO2 SOLUBILITY IN FELSIC MELTS

U (ppm)

in the

silicate

melt

Oxygen buffers

PERALUMINOUS PERALKALINEN i- NiO

H.M .

Cu 2O- C uO

NaF

HF

Peiffert et al., 1996

-4

-3

-2

0.6 1.30.90.80.7 1.1 1.21

-1

3

2

1

0

(Na+K+2Ca)/(Al.(Al+Si))

Ln(Σ

REE

/0.8

3)

metaluminous/peralkalineperaluminous

SHALES

MONAZITE SOLUBILITY IN SILICATE MELTS

from Montel, 1986

MANTLE

CONTINENTALCRUST

Cationic ratio : M = [(Na+K+2Ca)/(Al*Si)]

Zr

(pp

m)

Watson, E.B., Harrison, T.M., 1983. Zircon saturation revisited: temperature and compositional effects in a variety of crustal magma types. Earth Planet. Sci. Lett. 64, 295–304.

0.60

LnDZr(Zir/Liq) = -3,8 – [0,85.(M-1)]-12900/T750

500

250

00.80 1.00 1.20

930°C

860°C

800°C

750°C PERALKALINEPERALUMINOUS

ZIRCON SOLUBILITY IN SILICATE MELTS

METALUMINOUS

U - Th FRACTIONATION IN THE3 TYPES OF U – RICH ACIDIC MAGMAS

Peralkaline Peraluminous Metaluminous

graniteAv.

graniteAv.

graniteAv.

U (ppm)

Th (p

pm)

Complex U-Th-REE minerals

� Peralkaline complexes

� Carbonatites (Palaborwa, South Africa)

� Intrusive U deposits (IAEA classif.) Porphyry Cu

(high-K calc-alkaline granites)

U deposits related to crystal fractionation

EVOLUTION Of U-FRACTIONATIONDURING EARTH HISTORY

4 major periods :

1 : 4.6 – 3.2 Ga2 : 3.2 – 2.2 Ga3 : 2.2 – 0.4 Ga

4 : 0.45 - present

4.6 3.2 00.452.2

HADEAN ARCHEAN PROTEROZOIC PALEOZOIC

EVOLUTION Of U-GEOCHEMISTRYDURING EARTH HISTORY

14.6-3.2 Ga : HADEAN - PALEOARCHEAN

- thin mafic crust created by :

- Primitive mantle melting (7-21 ppb U)� basalts � TTG melts from partial melting of basalts

� Moderate magmatic U enrichments (few ppm in TTG)

� No or weak subduction processes

� Anoxic atmosphere

NO URANIUM DEPOSITS

magmatic differentiation+

mantle partial melting

Mantle

< 3.2 Ga 2.2 Ga 2.0 1.8 1.5

primitive

basaltsmagmatic differentiation

+basalt

partial melting

TTG

U < 1-2 ppm

EVOLUTION Of U-GEOCHEMISTRY DURING EARTH HISTORY : 1< 3.2 Ga : EARLY ARCHEAN

U(IV) U(VI)

magmaticdifferentiation

+mantle

partial melting

metasomatizedmantle

Subduction: oceanic crust

Singhbum Closepet …

U richcalc-alkaline

magmas

U richcalc-alkaline

magmas

KaapvalHigh-K granites

Start of subduction:recycling of

U-Th-K-rich crust materialstronger magmatic enrichment :

first K-U-Th granites

3.2 Ga 2.2 Ga 2.0 1.8 1.5

EVOLUTION Of U-GEOCHEMISTRY DURING EARTH HISTORY : 23.2-2.2 Ga : ARCHEAN & Upper PALEOPRO.

U(IV)

U-richperaluminous

magmas

Crust partialmelting

Tanco

pegm.

2.6 Ga2.8 Ga

PRE-3.1 Ga GRANITES - WITWATERSRAND BASIN (S.A.)

Intracratonic basin Large fluvio-deltaic

systems

3.09 < dep. < 2.7 Ga

Metamorphic peak : 2-3 kbar - 350 °C

Witwatersrand Basin South Africa

Frimmel, Earth-Sci Rev 70 (2005) 1–46

3A12.2-2.0 Gahigh pO2

uranyl ion [UO2]2+ in solution

U rich precursors :Organic-rich shelf sediments,

phosphorites

First chemical deposit(redox controlled) :

Oklo (Gabon) at 2.0 Ga

magmatic differentiation+

mantle partial melting

metasomatized

Mantle

Erosion-alterationin anoxic conditions

Subduction:oceanic crust +

sediments

Singhbum Closepet

GOE

Paleoproterozoicpassive margin

sediments

U-richperaluminous

magmas

Witwatersrand– Elliot Lake

Oklo

Uraninitedeposits in

quartz-pebbleconglomerate

U richcalc-alkaline

magmas

KaapvalHigh-K granites

Tanco

pegm.

U richcalc-alkaline

magmas

3.2 Ga 2.2 Ga 2.0 1.8 1.5

EVOLUTION Of U-GEOCHEMISTRY

DURING EARTH HISTORY

Oligomictic pebbly quartz arenite (reef), Vaal Reef, Stilfontein mine, Klerksdorp gold field1 cm

Minter, 2005

EVIDENCES FOR A REDUCED ATMOSPHERE < 2.3 Ga

2.2 Ga

Age distribution of banded iron-formations (after James, 1983), pyritic quartz-pebble conglomerates, continental red-bed sediments

Late Archean evolution (2.8 – 2.5 Ga)- rapid growth of the continents,

- decrease in mantle heat flux

� diminished outgassing of reduced species,

-proliferation of stromatolites

� large increase in O2-producing photosynthesis

- large-scale burial of organic matter in continental shelves

Higher O2 production, lesser O2 demand from sinks (red. gases, org. mat.)

� increased net supply of O2 to the atmosphere–hydrosphere

� CO2 drawdown due to large-scale carbonate platforms

Increase of : � pO2 in the atmosphere and pH of the hydrosphere

ARCHEAN ATMOSPHERECOMPOSITION

EVOLUTIONtwo theories :

• (A) ReducingpO2 (a) Kasting (1987, 2001)

(b) Rye & Holland (2000) others Pavlov et al. (2001a)

Kasting (2001)

(B) Oxidising(Ohmoto, 2004)

EVOLUTION Of U-GEOCHEMISTRYDURING EARTH HISTORY

3

2.2-0.45 Ga

high pO2 , uranyle ion [UO2]2+ -> in solution

3A12.2-2.0 Gahigh pO2

uranyl ion [UO2]2+ in solution

U rich precursors :Organic-rich shelf sediments,

phosphorites

First chemical deposit(redox controlled) :

Oklo (Gabon) at 2.0 Ga

magmatic differentiation+

mantle partial melting

metasomatized

Mantle

Erosion-alterationin anoxic conditions

Subduction:oceanic crust +

sediments

Kola

Singhbum Closepet

GOE

Paleoproterozoicpassive margin

sediments

U-richperaluminous

magmas

Witwatersrand– Elliot Lake

Oklo

syn-magmatic concentrations in pegmatoids

Crust partialmelting

Uraninitedeposits in

quartz-pebbleconglomerate

U richcalc-alkaline

magmas

KaapvalHigh-K granites

Tanco

pegm.

U richcalc-alkaline

magmas

3.2 Ga 2.2 Ga 2.0 1.8 1.5

EVOLUTION Of U-GEOCHEMISTRY

DURING EARTH HISTORY

Oklo - Okélobondo the first redox controlled U-depositsOklo - Okélobondo the first redox controlled U-deposits

100 m

W E

Okélobondo mine

151-2

3-67-9

13

10-16

OK84bis

FA sandstone

MineralizedC1 layer

FB black shales

ArcheanBasement

+ Reactionzones

Redox

boundary

EVOLUTION Of U-GEOCHEMISTRYDURING EARTH HISTORY

3A22.2-1.8 Ga

Oxydation of U accumulated as detrital uraninite

Huge production of organic matter �Carbon-rich shelf sediments (shungite) ; phosphorites ...

Strong U enrichment of post 2.2Ga epicontinental platform sediments :

Genesis of large U provinces : Wollaston belt (Athabasca, Canada),

Cahill Formation (N. Territory, Australia)Francevillian (Gabon)Talivaara (Finland)Shunga series (Onega Lake Russia) …

� Archean: Litsk area, NE Kola Peninsula, Russia, U pegmatoids

� “Hudsonian”s.l. (2.1-1.8 Ga): Wollaston + Mudjatik synsedimentary U enrichment : meta-arkoses (Duddridge L.), calcsilicates (Burbridge Lake & Cup L.) pegmatoids (Charlebois alaskites)

Steward Lake, Québec, CANADANorthern Québec, Ungava Bay and Baffin Island, U-pegmatoids, CANADA

Litsk district, Kola Peninsula, RUSSIA, U pegmatoids, Wheeler Basin, Colorado, USA: U- pegmatoids

Orrefjell, NORWAY: U-pegmatoidsSouthern FINLAND : Late orogenic potassic granites

Crocker Well, Olary Province, Flinders Range, South AUSTRALIASix Kangaroos area of Cloncurry-Mt. Isa District, AUSTRALIA

Nanambu, Nimbuwah, Rum Jungle complexes, Katherine-Darwin area, AUSTRALIA

� “Grenvillian” s.l. (1 Ga): Bancroft, ONTARIO : 4 mines (5,700 t U produced), Mt Laurier, Johan Beetz, Havre St Pierre, Sept Iles, Port Cartier, St Augustin QUÉBEC

�“Pan-African”: Rössing,SH,Husab,Valencia , IdaDome,Goanikontes

U-enrichment in metamorphosed epicontinental platform sediments

Shunga event huge amounts of organic matter incorporated by sediments in shelf & marginal sea environments � unprecedented increase of stromatolites at 2.05 Ga. Black shales :

� FB Formation of the Franceville basin, Gabon: up to 15 wt % OC

� Upper Zaonezhskaya Formation, Onega Lake, Russia. average : 25 wt %C over 600 m

3.35 wt %OC in average black shales

� Paleoproterozoic metasedimentary rocks metamorphosed to high grade: Wollaston belt in Saskatchewan,Canada, Cahill Formation (Northern Territory, Australia) = graphitic schist that during deformation became abundant graphite-rich fault zones (geophysical conductors)

� U content of these carbonaceous shales is anomalous, averaging 3.5 ppm to 10.8 ppm for the Francevillian, and up to 31 ppm (12−84 ppm) for the Onega basin.

� Average U content of younger black shale is also 30 ppm � indicate that by 2 Ga, oxidizing conditions were already sufficient to dissolve U as UO2+ and to deposit it in reduced environments.

Th and U analyses of shale show a significant decrease in their mean Th/U ratio from 4 at the Archean-Proterozoic boundary to 0.55 in the late Phanerozoic

Widespread deposition of black shale at 2.1 Ga related to increased weathering fluxes of nutrients such as P into the oceans triggered by global changes after major glaciations � increased availability of P have also stimulated photosynthetic O2 production

� first large phosphogenic event at 2.1 Ga in similar environments, also enriched in U (2.1 to 1.92 Ga Ludicovian epicontinental carbonaceous strata of Karelia.

Sea water became the largest U resource3.3 mg U / m3 (mg/m3= ppb)

= 4 billion t U

Exploitation technically possible, but costly :

Japanese scientists give prices > 250 $ / kg Uprobably > 1000 $ / kg to day

U in sea water(Arabian Sea)

Though dissolved O2 is low from 200 to1200 m, U concentration is uniform with depth.

No measurable change in U concentration in the water column during the seasons sampled

There is neither removal of U due to sub-oxic and denitrifying conditions nor addition of U from regeneration of biogenic particles in the intermediate waters

R. Rengarajan et al., Oceanologica Acta 26 (2003) 687–693

3.3 ppb

Example of the airborne gammaspectrometric map of Finland

The quantity of U transferred to sea water should vary

accordingly to the U contentof the eroded domains

U

U

The role of U content in the source area

IV (S) SYNSEDIMENTARY U DEPOSITS The metal is deposited within the sediments

during sedimentation processes

subdivided into 4 major types:

• IV.1 (SMs) Mechanical sorting Quartz Pebble Conglomerates (QPC)

• IV.2a (SRtm) Redox trapping in marine environments black shales.

• IV.2b (SRtc) Redox trapping in contin envir coal, lignite, peat bog, swamp

• IV.3 (SCcr) Crystal-chemical and redox trapping phosphorites

VERY LARGE LOW GRADE RESOURCES

Organic matter rich rocks & phosphorites considered as unconventional resources

� U deriving from sea water of surficial waters

IV (S) SYNSEDIMENTARY U DEPOSITS

•IV.2a (SRtm) Redox trapping in marine environments black shales

• IV.2b (SRtc) Redox trapping in contin envir coal, lignite, peat bog, swamp

Seawater only rarely becomes reducing(ex.: deep or bottom waters of the Black Sea, some fjords, Cariaco Trench)

Suboxic or anoxic conditions achieved at depth in marine sediments more frequently, in regions where there is a flux of high Corg to the seafloor as a result of high biological productivity in overlying surface water

Such areas occur most often on or near continental margins cover roughly 8% of the total area of the sea floor

U is present in seawater in the +6 state, generally as the very soluble uranyl tricarbonate species: UO2(CO3)3

-4

In reducing conditions its is reduced to the relatively insoluble U(IV)

IV.2a (SRtm) Redox trapping in marine environments black shales

U concentration in sediment and pore waters from the California

Shelf sediments

Consumption of 2.5% Corg at - 6 cm lead to suboxic conditions & reduction of U6+ to U4+

Organic-rich sediments tend to be rich in UThis reflects biological uptake of U or adsorption of

U on dead organic particles falling through the water column

This U may be released when the org. matter is remineralized in the sediment, producing high U contents in sediment pore water & consequently,

diffusion of U from sediments to seawater

On the whole, diffusion into sediments appears to be dominant

Barnes & Cochran (1990) diffusion into suboxic sediments removes 0.25 to 0.32 1010 gU/yrKlinkhammer & Palmer (1991) estimate a flux of 0.67 1010 gU/yr

Suboxic sediments are the largest sink for dissolved U in the oceans

The marine uranium budget

Sources (1010 g U/yr) Riverine Input 1

Amazon Shelf Sediments 0.14Total 1.14

Sinks (1010g U/yr) Sediments Oxic, deep sea 0.08

Metalliferous 0.14Underlying anoxic water 0.13Suboxic 0.25-0.32Corals and Molluscs 0.08

Ocean Crust Low temperature 0.23High temperature 0.04

Total 0.95-1.02

Barnes and Cochran (1990)

Mineralization ProcessLeventhal (1990), les eaux profondes euxiniques ont permis un piégeageefficace des métaux par réduction et préservation de la matière organique.Kalinowski et al. (2004): les fortes concentrations en U à Ranstad seraientdues en partie à des bactéries produisent des acides organiques à chainecourte et des ligands capables de modifier le pH et favoriser leur chélation.Teneur en matière organique pas toujours corrélée à la teneur en U.Plusieurs autres facteurs de concentration de l’U (Andersson et al, 1985) :• Importance de l’érosion de terrains granitiques riches en U situés en bordurede bassin (Harron and Associates, 2007)• existence d’un volcanisme acide avec émission de cendres, synchrone dudépôt des schistes noirs comme source additionnelle d’uranium ?• Incorporation plus efficace de l’uranium de l’eau de mer grâce au faible tauxde sédimentation par phénomènes de précipitation et adsorption.•Action biochimique de certaines algues vertes qui pourraient concentrer U

In the most enriched Upper Cambrian biozone (Peltura scarabaeoides Zone) the average concentrations of U (100 - 300 ppm)

inversely correlated to zone thicknessbed thickness variation = differences in the rate of deposition

High U levels generally found shorewards are interpreted to reflect a more vigorous bottom water circulation that promoted higher rates of mass-transfer across the sediment/ water interface relatively to the mud deposited

farther offshore. Highest levels of U (1000 - 8000 ppm) in discrete beds : KOLM

= resuspension of sediment in an anoxic water column that enhanced diffusive exchange between suspended particles and sea-

water.

Some crude oil, natural asphalt, and petroliferous rock are appreciably radioactive

U is associated with V, Ni, Cu, Co, Mo, Pb, Cr, Mn, and As.

U content of crude oil is much lower than the U content of the natural asphalt and oil extracted from petroliferous rock

U content of the ash of 78 samples ranges from 10 ppm to 10 %

U content of the total oil or asphalt ranges from less than 10 ppm to 3.24 %

Erickson, R. L., Myers, A. T., Horr, C. 1954. Association of uranium and other metals with crude oil, asphalt, and petroliferous rock. Bul. American Association of Petroleum Geologists. 38, 2200-2218

IV (S) SYNSEDIMENTARY U DEPOSITS

IV.3 (SCcr) Crystal-chemical and redox trapping :

Phosphorites

DIFFERENTS MATERIAL SOURCES IN THE SEDIMENTARY PHOSPHORITES

Shelf Margin

Phosphorites

High TOC

Mid-shelf

Fewer

Phosphorites

Low TOC

Upwellingwater

OM

Z

Hundre

ds o

f m

ete

rs

Silt-loaded continental

winds

5

Living organisms

1

1

2

4

5

Biochemical precipitation

Physical-chimical precipitation

Fluviatil particules supply

Eolian particules supply

3 42

3 Direct biological supply

6

6 Diagenetic evolution

SUBSTITUTION DANS LES SITES M

M10(ZO4)6(X)2

Ca2+ ↔ Sr2+, Mn2+, Pb2+, Ba2+, Eu2+

↔ Cd2+, Fe2+, Mg2+, Co2+, Ni2+

↔ Na+ 2M+ ↔ Ca2+ +

↔ 2M3+ + ZO44+↔ 2Ca2+PO4

3+

↔ REE3+, Y3+, Al3+ 2M3+ + ↔ 3Ca2+

↔ U4+, Th4+ M4+ + ↔ 2Ca2+

↔ U6+

The Cretaceous-Eocene Phosphate SeaU mineralization associated with phosphates are known since the PaleoproterozoicBut largest U resources with phosphates : late Cretaceous to Eocene (90-45 Ma)All deposited on carbonate platforms under the same paleolatitude (8-15º N) : S margin of Tethys Ocean: Turkey to Morocco, beyond Atlantic to Colombia & Venezuela Exceptional conditions of deposition, combining :(i) during Late Cretaceous creation of the Paleotethys Ocean : a continuous EW

seaway which merge with the Central Atlantic gulf already open during late Jurassic, by rifting of the Pangea between Laurasia and Gondwana

(ii) development of broad carbonate plateforms along S margin of the Tethys Ocean (iii) huge Late Cretaceous rise of the sea-level resulting from a global warming episode,both (i) and (ii) made possible a circum-equatorial westward oceanic current in the Tethys,

(iii) location of the Tethys at low latitudes, with the warmest climatic conditions(iv) dominant easterly winds producing a northward Eckman offshore transport of surface

waters inducing t upwelling of cold nutrient-rich waters all along the S Tethys shelves � huge biogenic productivity.

Morocco, with geological U resources of about 6.9 million tons U @ 50 - 150 ppm : ¾ of the world U resources associated with phosphates.

URANIUM CONTENT IN PHOSPHATES

URANIUM up to x100 ppm

In the apatite structure & inclusions

+ U minerals

Mean upper crust = 2,7 ppm

Recoverable during H3PO4 production

1980: 12% of world U was coming from the treatment of

phosphates

MAGMATIC APATITES

U => 3,4 %pds, Th => 15,9 %pds

D. Soudry et al. Chem. Geol.

189 (2002) 213–230

CEI S.AFRICA MOROCCO USA SENEGAL TOGORussia*Phalaborwa* Khouribga Florida

% Apatite 84 80 73 75 80 80

P2O5 38.9 36.8 33.4 34.3 36.7 36.7

CaO 50.5 52.1 50.6 49.8 50.0 51.2

SiO2 1.1 2.6 1.9 3.7 5.0 4.5

F 3.3 2.2 4.0 3.9 3.7 3.8

CO2 0.2 3.5 4.5 3.1 1.8 1.6

Al2O3 0.4 0.2 0.4 1.1 1.1 1.0

Fe2O3 0.3 0.3 0.2 1.1 0.9 1.0

MgO 0.1 1.1 0.3 0.3 0.1 0.1

Na2O 0.4 0.1 0.7 0.5 0.3 0.2

K2O 0.5 0.1 0.1 0.1 0.1 0.1

Organ. C 0.1 0.1 0.3 0.2 0.4 0.1

SO3 0.1 0.2 1.6 0.1 0.3

REE (ppm) 6,200 4,800 900 600

U3O8 11 134 185 101 124

As 10 13 13 11 18 12

Cd 1.2 1.3 15 9 53 53

Cr 19 1 200 60 6

Cu 37 102 40 13

Hg 33 0.1 0.1 0.02 0.2 0.6

Pb 11 10 17 5

Zn 20 6 200-400 www.efma.org/documents/

Phosphates with hexavalent U minerals, Agadir, Maroc

The uranium from unconventional resources results:

� Either SYN-MAGMATIC : concentration of U in residual melt by extreme fractional crystallization (peralkaline complexes and highly fractionated calc-alkaline granites)

� Or SYN-SEDIMENTARY : trapping mostly from sea water(sea water, blacks shales, phosphorites …) but also to a lesserdegree from surficial waters (coal, lignite, peat bogs …)

� Monazite placers

CONCLUSIONS